1. Field of The Invention
The present invention generally relates to the field of electronic audio equipment. More particularly, the present invention relates to the field of harmonics generators.
2. Description of The Prior Art
Harmonics generators are widely used in various applications of audio signal processing utilized for creating musical sound effects and enhancing sound quality. For example, a product made by Aphex Systems Ltd. called an "Aural Exciter" under U.S. Pat. No. 4,150,253 is based partly upon the use of a harmonics generator. Generally, a harmonics generator can be defined as a device which is used intentionally to produce harmonics of an input signal. Such a device may also produce spurious frequencies, for example beat frequencies, without violating the definition of a harmonics generator. A simple harmonics generator can be comprised of a full-wave rectifier circuit. The output signal from a full wave rectifier contains not only harmonics of the input signal, but also beat frequencies if the input signal is composed of typical audio waveforms which are composed of many frequency components.
In the prior art, non-linear circuits such as log amplifiers, rectifiers and multipliers are used as harmonics generators. These circuits all follow different harmonics generation laws depending on their input-output transfer functions. However, it can be generalized that the amplitude of the harmonics in the output signal is mainly a function of the input signal amplitude without regard to time. As a result, the harmonics which are developed resemble merely distortion products of the input signal. The usability of prior art harmonics generators for sound enhancement and music is therefore limited because the harmonics produced do not generally resemble harmonics of natural sounds and thus, are not pleasing to the human ear.
It is desirable to provide a harmonics generator that can generate harmonics which is not only a function of the amplitude of the input signal, but also a function of the time, to thereby better resemble the harmonics of natural sounds for sound enhancement and music.